Competing impacts of internal pores dissolution and external compression on the permeability evolution during the infiltration of weakly acidic fluids

In the water conservancy and hydropower projects, the infiltration of weakly acidic groundwater has an essential effect on the permeability evolution of sandstones. Previous studies considered that the permeability was only positively proportional to the volume of dissolution pores. This ignored the coupling effects of external compression on internal pores dissolution and inevitably overestimated permeability, which could lead to the misunderstanding of flow mechanisms in actual geotechnical engineering. In this study, a "multi-physical coupling permeability test platform for rocks" was used to conduct the permeation-dissolution experiment on sandstones. Firstly, the evolutions of exudate ion concentration, strain, and seepage rate in sandstone specimens were measured. Secondly, the mechanical degradation of sandstones by chemical dissolution was analyzed through the obtained experimental data. Finally, an improved permeability model was proposed to describe the competing effect of internal pores dissolution and external compression. It was found that (1) Although the water-rock reaction increased the dissolved porosity only by 0.42%, the mechanical properties of the sandstone were significantly weakened; (2) The effect of pores dissolution on permeability enhancement was suppressed by mechanical weakening; (3) The improved permeability model was consistent with the experimental data. This indicated that the improved permeability model could accurately characterize the competing effect between internal pores dissolution and external compression.